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Full text of "mit :: whirlwind :: Magnetic Drum System WWI Jun58"

l&vlsion 6 « Lincoln Laboratory 

Ilassachusetts Institute of Technology 

Lexington 73» Massachusetts 



IliMlOFFlCli il£Ml,RAWiJuH 



SUBJECTS ilAGIfiSTIC DRUi-i i5J3TiHl D WWI 



Dates 30 June 1958 (Corrected) 

The Me chanics of Lisabling and lfri ahLin g the Write Funct ion 

At tines it is desirable to disable the write function on one 
or more groups of the auxiliary drum so that the information recorded on 
that group is permanent This is now being done on group 11 which contains 
the input progranio The following paragraphs describe the method used to 
disable the write function and explains how to enable xjriting is the in« 
formation must be changed on a disabled group 

As mentioned in the section on write group selection^, we use two 
methods of write switching the auxiliary drum Therefore., we must perform 
two tasks to disable the write function in a group or to enable x-jriting 
once the group lias been locked in reado 

The drum bays in Room lf>6 are numbered from north to southo The 
auxiliary system comprises bays 1 through 3 with the drum itself being lo« 
cated in bay 3o The jacks in which are mounted the plug^in units are 
numbered from top to bottom and from right to lefto A jack layout of each 
bay is mounted inside the bay door© The tubes on each plug«dn chassis 
are numbered from top to bottom The left side of the unit contains tubes 
CO. through 08 5 the right side of the chassis contains tubes 21 through 29 o 
(These numbers refer to tube positions.) and there may be some empty posi« 
tions on certain chassis ) 

In order to disable a group., we must remove two type 03 chassis 
which contain the gate writer amplifiers for each digit of the group 'bo be 
disabled^ and we must remove two additional tubes which comprise the writer 
for the parity digit for that group 



The irriters for the individual dibits for each group are 
contained in two type 03 chassis located in bay 1, jacks 01 through 2lu 
There are thirty tiro writers to a group 5 a one writer which is assigned 
the odd socket^ and a zero writer assigned the even sociccto For each 
digits tlie tube layout and identifying numbers., which permit you to 
select the tubes to be removed or inserted to disable or enable the 
write function for a particular group^ are shown in figure lo 

The writers for the parity digits are located in Bay 1* The 
chassis containing the. writers are mounted in J26 and J27* JSach chassis 
contains eight writers o Tne writers for groups Q«»7 are on the chassis in 
J26o The writer's for groups 6VL1 are on the chassis in J27» There are 
four spare writerso To disable or enable a parity digit for one groups 
two tubes must be removed or inserted© The tube layout and identifying 
numl^ers for the parity digits are shown in figure 2© 
To summarize £ 

lo If you wish to disable a group so that it is no longer 
possible to write in its 

a tiim off the voltages to the drum system l#r pushing 
the drum stop button., pulling down the bar switch 
and then pushing the drum start button^ in Bay 3q 
b pull out the two type 03 chassis for the group to be 

disabled© 
Co pull out the two tubes for the parity digit for the 

group to be disabled© 
do turn on the voltages to the drum system by pushing 
the drum stop button., pushing up the bar switch and 
then pushing the drum start button., in Bay 3© 
2o If you wish to enable a previously disabled group so that 
information can be recorded on it© 

a© turn off the voltages to the drum system by pusliing 
the drum stop button^ pulling down the bar switch and 
then pushing the drum start button., in Bay 3° 



a 3 c 



bo put in the two typo 03 chassis for the group to bo 

enabledo 
Co put in the two tubes for the parity dir.lt for the group 

to be enabledo 
do Turn on the volta'^es to the drum system by pushing the 
drun stop button> pushing up the bar switch and then 
pushing the drum start button $ in Bay 3o 
It is very toortant tliat bhu positive voltages are turned off 
to the drum system whenever inserting or reiioving tubes Failure to turn 
off the control switch may result in writing between the slots, which re« 
quires erasure of the drum trades Q 



Attached s Figure 1 
Fif'ure 2 Q 



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MY I 
WRITERS FOR ALL GROUPS 




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FIGURE lo A 



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WRITERS FOR R\RITT DIGITS 



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Notes 401 tubes ?AK? 



Division 6 « Lincoln laboratory 

Massachusetts Institute of Technology 

Lexington 73j> Massachusetts 

INTEROFFICE MEMORANDUM 



SUBJECTS MAGNETIC DRUM S3BTEM, WWX 
ERASING THE DRUM TRACKS 

Dates 18 June 1958 (Corrected) 

1 Determining the. Nesd for Erasure 

3h case of a drum parity alarm the register at fault should be 
examined,. This is done fcy the use of the drum«monitor scope in TC*»2<> A 
visual check of all the tracks in a group which has been giving trouble 
will frequently reveal writing between the slots© If the register at fault 
is not known-, a check should be made with the scope sweep on If milliseconds o 
This will give a picture of the complete track because 17 milliseconds is 
the time required for one drum revolution 

The writing between the slots may be one of two general types o 
Both of these defects show up as irregularities in the envelope of the 
readout signal which appears on the scope in TC~2o A small section of this 
waveform is shown in Figure la as it should appear ^hen a series of ones 
or aeroes have been stored on the drum surface© Long time variations in 
amplitude are not important^ but sudden changes in signal amplitude may 
indicate writing between the slots If the writing is only between one 
or two slots^ the waveform may approximate that shown in Figure Ib c Writing 
between many slots usua!3y shows up as a decaying exponential as shown in 
Figure le e 

If the register at fault is known^ then an expanded sweep should 
be usedo The scope should be synchronised on "sync coincidence" and in«? 
terisification should also be on "sync coincidence"* The push button switches 
at the side of the scope are used to select scope sync and intensification* 
The register which is at fault should be set in the toggle switches at the 
top of the scope in TC2 This is the register which will be intensified 
on the scope*, Examination of the individual digits is made ty selec&ng the 
proper push button directly below the register selectors© The waveform 
which would appear in a "one" were stored in the selected register (with 



(Page 2j 

sefos on either side of it) is shown in Figure 2a. The dark spot represents . 
the scope intensification* If there is writing between the slots^ this spot 
will appear somewhere near the scope center line (see Figure 2b) c 

If writing between the slots is determined to have occurred by 
either of these methods^ then the track at fault must be erased* If one 
digit of the information tracks shows a bad track waveform^ check all other 
digits in the same group* If one digit of the parity tracks has writing 
between the slots g check all other parity digits for the other groups** 

2 The Mechanics of Erasing 

If the spurious writing is not serious^ it may be possible to 
reduce its effect ty running Tape 363lw Suppress the drum parity until the 
program has cycled through all groups at least twice* Then try to run the 
program with the drum parity check in and a «60V margin on line 2 0o o If 
this runs 5 the drum should operate satisfactorily© Should this procedure 
fail* more "elaborate steps must be taken* 

When we erase the drum surface^ we establish* as nearly as possible^ 
a neutral surface This is done by applying a 60 cycle voltage to the head 
and varying the voltage from zero up to a value which will give its about 
1 ampere of current through the head 5 and then reducing the voltage back to 
aero© During the. erase operation the power to the drum should be turned o££ 
to prevent the recording of a standing wave on the drum; surface due to an 
undesirable relation between the drum speed and line frequency* 

The drum erase circuit is on a chassis which is usually located 
on the air»conditioning ducts between the two drum bays, ^ho^tsops to bQ 
followed in erasing are enumerated below: 

1* Remove the head cable from the track to be erased* (See nest 
section for method of determining location of track once digit 
and group are known.) 

2* Connect the head cable from the drum»erase chassis© 

3o Push the STOP button on the drum motor control switch* 

ho Push the button on the front of the drum erase chassis and 
wait for a complete cycle or until the motor stops * 

£o Push the START button on the drum motor control switch* 

6* Disconnect the head cable from the drum-erase chassis and 
connect the original head cable. (Ee careful to line keyway 
up properly©) 

7* Go ti> • the next track if there is one* 



(Page 3o) 

The selected tracks are now erasedo Run the drum check program 
T»36lU through one cyelSo If there are any alarms^ repeat until the program 
will go through a complete cycle without alarm. 

3» Identifying the Drum Tracks 

The tracks on the drum are arranged in a spiral around the cover* 
THE FIRST SPIRAL CONTAINS CONTROL TRACKS AND SHOUli) NEVER BE ERASBDo The 
information heads start on the second spiral*, Each turn of the spiral con- 
tains the heads for one group a 

A map of the drum tracks is given in Figure 3° The digits are 
numbered in order around the spiral* The digit 7 of ' group 5 is track 90« 
Once the digits which have spurious writing on the track have been located 
by means of the monitor scope in TO&j they can be located on the. drum by 
use of the diagram in Figure 3o 

ALL TRACKS MARKED IN RED ON FIGURE 3a SHOULD METER BE ERASED UNLESS PROPER 



KEnnBMa 



AUTHORIZATION HAS BEEN GRANTED,, 



Attached i Figure 1 P 
Figure 2© 
Figure 3o 



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